Background: Twenty-four-hour serum cortisol secretion is a sensitive parameter for the assessment of the pituitary-adrenal function of asthmatic children treated with inhaled corticosteroids. This study was undertaken to determine the effect of the long-term administration of inhaled budesonide on 24-hour cortisol production in young children with asthma. Methods: We studied 11 children, aged 7 to 12 years, with severe perennial asthma. All had been receiving 100 μg of inhaled budesonide twice daily, administered with a spacer device, for 3 to 5 years. Serum cortisol concentration was measured at 8:00 AM, 60 minutes after intravenous administration of 0.25 mg of corticotropin, and every 30 minutes for 24 hours in an open-design study. Urinary cortisol secretion was measured by 24-hour urine collection. All determinations were made with a radioimmunoassay kit. Results: The individual morning serum cortisol concentration and the serum cortisol concentration at 60 minutes after corticotropin stimulation were within normal limits in all children. The 24-hour urinary cortisol excretion was also normal. The individual 24-hour serum cortisol concentration showed a normal pattern in all children, with no evidence of nocturnal suppression of serum cortisol concentration. Conclusion: Prolonged (3 to 5 years) administration of 200 μg/day of inhaled budesonide in young children with severe asthma does not impair pituitary-adrenal function, even according to the sensitive test for 24-hour serum cortisol secretion. (J ALLERGY CLIN IMMUNOL 1995;96:874-8.)